WASHINGTON (AP) -- A new federal report is the most exhaustive and perhaps even easiest-to-read look at what global warming will to do the United States, say experts who strongly support it.

The report, required by federal law, is "the most comprehensive assessment ever done on how climate is affecting the United States," said University of Illinois climate scientist Donald Wuebbles, a study author. White House counselor John Podesta called it authoritative and "a tremendous undertaking."

But conservative think tanks, Republican elected officials and industry officials called the report alarmist. House Science Committee Chairman Lamar Smith of Texas said, "The Obama administration feels compelled to stretch the truth in order to drum up support for more costly and unnecessary regulations and subsidies."

"This is more a political document than it is a scientific document," said Charlie Drevna, president of the American Fuel and Petrochemical Manufacturers, using a phrase used repeatedly by critics Tuesday.

But scientists who study the issue say that's not correct. Two organizations of scientists in the field -- the American Meteorological Society and the American Geophysical Union -- praised the study, its conclusions and the scientific way it was conducted.

A team of 253 scientists, engineers, government officials, utility leaders, lawyers and other experts -- nearly half of whom work at universities -- spent about three years writing the report. It came out of 70 different workshops and then had about 60 outside reviewers. It is based mostly on peer-reviewed science and contains 3,096 footnotes with references to studies and reports.

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After a draft was released in 2013, the public, more scientists, 13 federal agencies and the National Academy of Sciences reviewed the report. There were more than 4,000 public comments on it. It was extensively rewritten, mainly to make it a bit shorter and easier to read, said lead author Gary Yohe of the Wesleyan University in Connecticut.

The National Academy concluded: "Given the current state of the science and the scope of resources available, we believe the NCA did a reasonable job of fulfilling its charge overall" and the report "should prove to be a valuable resource, as a summary of the state of knowledge about climate change and its implications for the American people." Rep. Smith, in a press release, said the academy was "critical" of the report.

The 840-page report divides the United States into eight regions, including coastal areas, looking at impacts in each area. The report has 30 chapters, several appendices and 12 "key findings."

"There are so many reports coming out, it is hard to decipher (from a public standpoint) what to pay attention to," University of Georgia meteorology professor Marshall Shepherd, who wasn't part of the report but is past president of the American Meteorological Society, said in an email. "Since this is U.S. focused, Americans should take notice of the detailed information, given at a regional level, on how the changes affect their lives."